Umm al-Ḥuwayrith and Umm al-Rabāb are two distinct women's names or teknonyms. Wa-jāratihā adds their relationship as neighbors. Bi-Maʾsal is a place name and should not be translated as though it were an ordinary descriptive noun.
ExpressionMeaning or relation
Umm al-ḤuwayrithTeknonym of a woman recalled in the poem
JāratuhāHer neighbor; pronoun refers to the first woman
Umm al-RabābTeknonym of the second woman
MaʾsalThe named locality associated with the episode
The proper names turn general romantic recollection into memory anchored to particular people and a particular place.